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ESO Y4A · Mathematics
coordinate geometry · Coordinate geometry

Coordinates

A drone's GPS doesn't say "turn slightly left": it gives two numbers, a position $(x, y)$. And when the drone flies from one point to another, that flight can also be described with two numbers: how far it moves horizontally and how far it moves vertically. We call that "flight" a vector, and with it you will solve almost everything in this topic: distances, midpoints, lines…

Before you start, make sure you know: Pythagoras' theorem (2nd ESO)
Before you start, make sure you know: Plotting on the Cartesian plane (2nd ESO)

The plane, once more

You already know the Cartesian plane from earlier years: two perpendicular axes, and a point $P(x, y)$ is plotted by counting $x$ horizontally and $y$ vertically from the origin $O(0,0)$. What is new in this topic is that you will use this map for more than plotting points: you will measure and calculate on it.

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Find the exact distance between the points $P(1, 4)$ and $Q(-5, -4)$ in the Cartesian plane.

Find the exact distance between the points $P(1, 4)$ and $Q(-5, -4)$ in the Cartesian plane.

Solve

The vector of a displacement

Vector AB on the Cartesian plane, breaking the movement from A to B into a horizontal and a vertical displacement. A(−2, 1) B(4, 9) +6 +8
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Calculate the components of the vector $\vec{AB}$, knowing that its initial point is $A(-3, 5)$ and its terminal point is $B(4, -2)$.

Calculate the components of the vector $\vec{AB}$, knowing that its initial point is $A(-3, 5)$ and its terminal point is $B(4, -2)$.

Solve

The magnitude of a vector

The vector $\vec{AB} = (v_1, v_2)$ forms a right-angled triangle with the axes: $v_1$ and $v_2$ are the legs. By Pythagoras, its magnitude (length) is:

$$|\vec v| = \sqrt{v_1^2 + v_2^2}$$ Right-angled triangle formed by the horizontal and vertical components of a vector, used to derive its magnitude with Pythagoras' theorem. |v| v₁ v₂
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Determine the magnitude of the vector $\vec{v} = (6, -8)$. Simplify the result if possible.

Determine the magnitude of the vector $\vec{v} = (6, -8)$. Simplify the result if possible.

Solve
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Given the vector $\vec{w} = (k, 3)$, calculate the possible values of the parameter $k$ such that the magnitude of this vector is exactly $5$.

Given the vector $\vec{w} = (k, 3)$, calculate the possible values of the parameter $k$ such that the magnitude of this vector is exactly $5$.

Solve

Distance between two points and midpoint

The distance between $A$ and $B$ is simply the magnitude of the vector $\vec{AB}$:

$$d(A, B) = |\vec{AB}| = \sqrt{(b_1 - a_1)^2 + (b_2 - a_2)^2}$$

And the midpoint $M$ of the segment $AB$ has as its coordinates the mean of those of the end points:

$$M = \left(\frac{a_1 + b_1}{2},\ \frac{a_2 + b_2}{2}\right)$$ Segment bounded by the end points P and Q, marking its midpoint M, equidistant from both. P Q M
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A forest surveillance drone takes off from point $A(-2, 1)$ on a grid map with units in kilometres. It flies in a straight line to point $B(4, 9)$ to inspect a…

A forest surveillance drone takes off from point $A(-2, 1)$ on a grid map with units in kilometres. It flies in a straight line to point $B(4, 9)$ to inspect a suspicious clearing, and from there moves directly to point $C(10, 1)$ to examine a shelter. Calculate the total distance covered by the drone during this journey.

Solve
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The geometric centre of a circular ice rink is located at coordinates $C(2, -3)$. If one end of the rink, where the entrance gate is located, is at point $A(-1, 1)$,…

The geometric centre of a circular ice rink is located at coordinates $C(2, -3)$. If one end of the rink, where the entrance gate is located, is at point $A(-1, 1)$, find the coordinates of the diametrically opposite end $B$ and calculate the total diameter of the rink.

Solve

Collinear points and symmetric points

Three collinear points A, B and C on the same line, showing vectors with the same direction. A B C

A point $A'$ is the symmetric point of $A$ with respect to a centre $P$ when $P$ is the midpoint of $A$ and $A'$: $A' = 2P - A$.

Practice★☆☆Not started
Find the coordinates of the point $A'$, knowing that it is the reflection of $A(-2, 6)$ in the centre of symmetry $P(1, 1)$.

Find the coordinates of the point $A'$, knowing that it is the reflection of $A(-2, 6)$ in the centre of symmetry $P(1, 1)$.

Solve
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An architect is designing a suspension bridge in which three of the main cable anchors must be perfectly collinear to ensure correct tension. On the construction plan,…

An architect is designing a suspension bridge in which three of the main cable anchors must be perfectly collinear to ensure correct tension. On the construction plan, their coordinates are $P(-3, 2)$, $Q(1, 4)$ and $R(a, 7)$. Calculate the value of parameter $a$ so that the structure is stable.

Solve

Summary

See all the exercises in this section